With bonfire night approaching we are all waiting in anticipation for the night sky to be lit up by an explosion of fireworks. In a slightly different take on manmade fireworks, we take a look at the science behind some of earth’s strange and beautiful natural light displays.
The Aurora, named after the Roman goddess of dawn, is a stunning and fascinating display that is most easily observed at high latitudes near the magnetic poles. This is because the solar winds responsible for the effect are accelerated along earth’s magnetic field lines. Solar winds are a flow of charged particles from the sun that collide with gas atoms giving them the energy to emit light. It is this light that forms the entrancing colours that are painted across the sky.
The variety of colours within the aurora are created by different atoms at different altitudes. Oxygen contributes the common green when it is at lower altitudes, but at higher altitudes the rarer red. Nitrogen is also responsible for two colours, blue and also a purplish-red.
Although visible aurora displays are usually restricted to northern and southern hemispheres, this year was an exception, with many of us in the UK being lucky enough to get an unusual glimpse of the aurora. These displays are pretty rare, however, and are only made possible due to strong geomagnetic storms. Auroral activity runs in 11 year cycles, with this year being the year of maximum activity. Meaning: you haven’t yet missed your chance of seeing it here in the UK.
If, like many, seeing the Aurora Borealis is on your bucket list, you can maximise your chances of seeing it by monitoring geomagnetic activity on the internet using ‘Aurora Watch’. If there is a strong chance of a sighting, then your best bet lies in the countryside or somewhere with little light pollution, between the times of 10pm and 2am. The geomagnetic storms that enable us to see these entrancing shows can have a more sinister side, however. The increase in charged particles interacting with Earth’s magnetic field can disrupt power grids, satellite communications and even radio signals.
Talking of sinister consequences, another strange and dramatic light display that the earth’s systems give us is ball lightning, which has been known to not only cause damage but in some cases fatalities. Throughout history there have been reports of ball lightning, which refer to strange luminous spheres that appear during a thunderstorm. These sightings do have inconsistencies which have led to confusion over the reliability of the reports.
Although it doesn’t prove their existence in nature, the balls have successfully been reproduced in a laboratory. Scientists have attempted to explain the phenomenon and several theories exist to explain their occurrence. One of the main theories is that ball lightning is created by slowly burning particles of silicon formed in a lightning strike. A new theory announced this summer contradicts this and uses standard equations for the motion of electrons and ions. It is the first theory to try and explain how the balls can appear to pass through glass, resulting in globes of light in people’s homes or in aeroplane cockpits. However, due to their rare and unpredictable existence, little data has successfully been taken of ball lightning, so that the existence of these fascinating balls remains unconfirmed and their possible origins a mystery.
Lightning balls are strangely not the only unverified flaming balls, fireballs have also been rumoured to rise from Thailand’s Mekong River. Known as the Naga fireballs, they are described as glowing balls which rise from the river high into the air. The largest number of reports occur around this time of year, so if you’re desperate to find out if they are real you’re going to need to get a move on!
Perhaps the simplest (but still most magical) moving light that you can observe in the night sky is a shooting star. Shooting stars have long been a source of inspiration for a wide range of professions from scientists to songwriters and philosophers. Lots of us are not embarrassed to admit we get excited by the sight of a shooting star and will immediately wish on it. Although I’m sure most of us will be embarrassed to learn that actually in some cases we have instead been wishing upon a satellite! To avoid any confusion the key way of telling the two apart is speed. A shooting star will flash across the sky in a matter of seconds, where as a satellite will take several minutes.
The magic and appeal of shooting stars is, if anything, increased by understanding their true nature. Shooting stars are not as the name may suggest stars, they are in fact meteors. When you see a shooting star what you are actually observing is a meteor from outer space burning up as it enters our atmosphere. In some cases meteors are so large that they are not fully burnt up and their remnants fall to earth, landing as meteorites. These again pose a massive potential threat: in fact, if the asteroid was large enough, the threat could be apocalyptic. So, like Aurora Borealis, the seemingly innocent shooting star has a darker side.
Hope you all enjoy bonfire night and good luck to you all in seeing these amazing, but potentially catastrophic natural light extravaganzas!